The present invention relates to a device for filtering and treating molten metal.
According to EP-A-0 578 517, a device for filtering and treating molten metal includes a set of at least two filtering plates, consisting of a refractory mineral material and having through-holes for the passage and the filtration of the molten metal, such plates being kept at a certain distance apart by means of peripheral walls so as to provide, between them, a cavity receiving an insert made of a treating material for said molten metal and having such a shape that, as seen in the direction of flow of the liquid metal, the insert leaves at least one uncovered area on the filtering plates.
The area of the first filtering plate (upstream), which is not covered by the insert of treating material, includes free filtering holes, allowing the molten metal to enter the cavity, contact the treating material of the insert and flow around the insert before leaving the cavity through the free filtering holes in the second filtering plate (downstream).
It can therefore be noted that the molten metal flows freely through the device as soon as the casting process begins, after having been brought in contact with the treating material present in the device cavity, with the result that a quite homogeneous treatment of the molten metal can be obtained right from the beginning and up to the end of the casting of said metal.
Such a device is suitable for a prefabrication by the filter supplier, according to the end user's requirements.
However, the end user, as a general rule a foundry, has two conflicting requirements.
On the one hand, based on the fact that the weight of a given treating material must be a known fraction of the weight of the molten metal-flowing through the device during a predetermined casting process, the user requires devices with different predetermined respective weights of treating material, constituting a set. Such a set may range, for instance as regards an inoculating material for the casting of spheroidal-graphite cast iron, from ten grams to 150 grams or more, in successive steps 10 grams by 10 grams, or 20 grams by 20 grams.
Besides, various treating materials are used depending on the nature of the molten metal to be treated, such various treating materials having different densities and being used in different proportions in relation to the weight of the molten metal to be treated.
On the other hand, and on standardisation grounds for the equipment used, the user wants to limit as much as possible the number of devices with various sizes, necessary for meeting his requirements.
Therefore the Applicant has been led to investigate the feasibility of placing, in the cavity of a device used for filtering and treating molten metal, different quantities of various treating materials. Some tests, carried out by the Applicant, have revealed, in certain cases, a decrease in the quality and/or homogeneity of the treatment of molten metal in the course of a casting process.